1. Field of the Invention
The present invention relates to a gas generator arrangement and more particularly relates to a gas generator arrangement adapted to generate gas to inflate an air bag.
It has been proposed to provide an air bag in a motor vehicle, the air bag being adapted to be inflated in the event that an accident should arise, the inflated bag providing protection for the driver of the vehicle or a passenger in the vehicle.
It is a requirement for an air bag in a motor vehicle that the air bag should operate quickly in the event that an accident arises. Thus, the air bag must be fully inflated within a very brief period of time if the air bag is to provide protection in a satisfactory manner. Also, the air bag must be very reliable. In some cases, the air bag has totally replaced safety belts, and it is thus imperative that the air bag should be inflated whenever an accident arises. A further factor that must be taken into account when designing an air bag arrangement is that the air bag may remain un-operated for a very long period of time, but must operate reliably whenever an accident occurs. Thus, a motor vehicle incorporating an air bag may be driven for twenty years or more, and the air bag must remain in an operative state for the whole of that period of time.
2. Description of the Related Art
In many prior proposed air bag arrangements, the air bag is associated with a crash sensor which consists of an electronic unit which, when subjected to a predetermined deceleration, indicative that an accident is occurring, transmits an electrical signal to an electrical ignite, present in the gas generator associated with the air bag.
However, it has now been proposed, as disclosed for example in WO 93/07440, to generate an ignition pulse not by using an electrical system, but instead by using a pyrotechnic trigger unit, which can generate an ignition pulse which is transmitted by means of a shock tube (such as the shock tube sold under the Trade Mark NONEL) to the gas generator of an air bag. Such a system is therefore independent of electrical power.
From the point of view of stability, it is important for the elements of such a system to be hermetically sealed or substantially leak-tight so that the elements can be stored and handled without any problems arising due to the ingress of moisture. It is also important for the gas generating substances within the gas generator to be ignited correctly to avoid an undesirable pressure rise curve.
The present invention seeks to provide an improved ignition device for use with a gas generator .